Inter prediction using polynomial model

ABSTRACT

A method for video processing includes performing a conversion between a current video block and a bitstream representation of the current video block using an inter-prediction coding scheme based on an n-order polynomial model using a first variable associated with the current video block, where n is an integer greater than or equal to zero, wherein the conversion includes generating the current video block from the bitstream representation or generating the bitstream representation from the current video block; and performing illumination compensation for the current video block using the n-order polynomial model during the conversion.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation of international No. PCT/CN2019/127580, filed on Dec. 23, 2019, which claims the priority to and benefits of International Patent Application No. PCT/CN2018/122712, filed on Dec. 21, 2018. All the aforementioned patent applications are hereby incorporated by reference in their entireties.

TECHNICAL FIELD

This document is related to video coding technologies.

BACKGROUND

Digital video accounts for the largest bandwidth use on the internet and other digital communication networks. As the number of connected user devices capable of receiving and displaying video increases, it is expected that the bandwidth demand for digital video usage will continue to grow.

SUMMARY

The disclosed techniques may be used by video decoder or encoder embodiments for in which interpolation is improved using a block-shape interpolation order technique.

In one example aspect, a method for processing video is disclosed. The method includes performing a conversion between a current video block and a bitstream representation of the current video block using an intra-prediction coding scheme based on an n-order polynomial model using at least one variable associated with the current video block, where n is an integer greater than or equal to zero, wherein the conversion includes generating the current video block from the bitstream representation or generating the bitstream representation from the current video block.

In another example aspect, a method for processing video includes performing a conversion between a current video block and a bitstream representation of the current video block using an intra-prediction coding scheme based on an n-order polynomial model using a first variable associated with the current video block, where n is an integer greater than or equal to zero, wherein the conversion includes generating the current video block from the bitstream representation or generating the bitstream representation from the current video block, wherein cross-component prediction is applied by using the n-order polynomial model.

In still another example aspect, a method for processing video is disclosed. The method includes performing a conversion between a current video block and a bitstream representation of the current video block using an inter-prediction coding scheme based on an n-order polynomial model using a first variable associated with the current video block, where n is an integer greater than or equal to zero, wherein the conversion includes generating the current video block from the bitstream representation or generating the bitstream representation from the current video block; and performing illumination compensation for the current video block using the n-order polynomial model during the conversion.

In yet another example aspect, a method for processing video is disclosed. The method includes performing a conversion between a current video block and a bitstream representation of the current video block using an inter-prediction coding scheme based on an n-order polynomial model using a first variable associated with the current video block, where n is an integer greater than or equal to zero, wherein the conversion includes generating the current video block from the bitstream representation or generating the bitstream representation from the current video block; and performing multi-hypothesis inter prediction using the n-order polynomial model during the conversion.

In yet another example aspect, the above-described methods may be implemented by a video decoder apparatus that comprises a processor.

In yet another example aspect, the above-described methods may be implemented by a video encoder apparatus comprising a processor for decoding encoded video during video encoding process.

In yet another example aspect, these methods may be embodied in the form of processor-executable instructions and stored on a computer-readable program medium.

These, and other, aspects are further described in the present document.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an illustration of intra prediction modes.

FIG. 2 shows an example of reference samples for wide-angular intra prediction.

FIG. 3 shows an example of discontinuity in case of directions beyond 45 degrees.

FIG. 4 shows examples of samples used by position dependent intra prediction combination (PDPC) applied to diagonal and adjacent angular intra modes.

FIG. 5 shows an example of using a polynomial model for intra prediction.

FIGS. 6A-6H show examples of neighboring samples used for deriving parameters of a polynomial model.

FIGS. 7A-7K show examples of neighboring samples used for deriving parameters of a polynomial model.

FIG. 8 is a block diagram of an example of a video processing apparatus.

FIG. 9 shows a block diagram of an example implementation of a video encoder.

FIG. 10 is a flowchart for an example of a video bitstream processing method.

FIG. 11 is a flowchart for an example of a video bitstream processing method.

FIG. 12 is a flowchart for an example of a method for processing video.

FIG. 13 is a flowchart for an example of a method for processing video.

DETAILED DESCRIPTION

The present document provides various techniques that can be used by a decoder of video bitstreams to improve the quality of decompressed or decoded digital video. Furthermore, a video encoder may also implement these techniques during the process of encoding in order to reconstruct decoded frames used for further encoding.

Section headings are used in the present document for ease of understanding and do not limit the embodiments and techniques to the corresponding sections. As such, embodiments from one section can be combined with embodiments from other sections.

1. Summary

This document is related to video/image coding technologies. Specifically, it is related to intra prediction. It may be applied to the existing video coding standard like HEVC, or the next generation video coding standard Versatile Video Coding (VVC) to be finalized. It may also be applicable to future video coding standards or video codec.

2. Brief Discussion

To explore the future video coding technologies beyond HEVC, Joint Video Exploration Team (JVET) was founded by VCEG and MPEG jointly in 2015. Since then, many new methods have been adopted by JVET and put into the reference software named Joint Exploration Model (JEM). The Joint Video Experts Team (also named as JVET)—a collaborative team formed by the ITU-T Study Group 16 Video Coding Experts Group and ISO/IEC JTC1 SC29/WG11 (Moving Picture Experts Group, MPEG)—has launched a project to develop a new video coding standard to be known as Versatile Video Coding (VVC). Work on the new VVC standard commenced at a meeting of the Joint Video Experts Team in San Diego, U.S., 10-20 Apr. 2018.

FIG. 9 is a block diagram of an example implementation of a video encoder.

2.1 Intra Mode Coding with 67 Intra Prediction Modes

To capture the arbitrary edge directions presented in natural video, the number of directional intra modes is extended from 33, as used in HEVC, to 65. The additional directional modes are depicted as arrows in FIG. 1, and the planar and DC modes remain the same. These denser directional intra prediction modes apply for all block sizes and for both luma and chroma intra predictions.

Conventional angular intra prediction directions are defined from 45 degrees to −135 degrees in clockwise direction as shown in FIG. 1. In VTM2, several conventional angular intra prediction modes are adaptively replaced with wide-angle intra prediction modes for the non-square blocks. The replaced modes are signaled using the original method and remapped to the indexes of wide angular modes after parsing. The total number of intra prediction modes is unchanged, i.e., 67, and the intra mode coding is unchanged.

In the HEVC, every intra-coded block has a square shape and the length of each of its side is a power of 2. Thus, no division operations are required to generate an intra-predictor using DC mode. In VVV2, blocks can have a rectangular shape that necessitates the use of a division operation per block in the general case. To avoid division operations for DC prediction, only the longer side is used to compute the average for non-square blocks.

2.2 Wide-Angle Intra Prediction for Non-Square Blocks

Conventional angular intra prediction directions are defined from 45 degrees to −135 degrees in clockwise direction. In VTM2, several conventional angular intra prediction modes are adaptively replaced with wide-angle intra prediction modes for non-square blocks. The replaced modes are signaled using the original method and remapped to the indexes of wide angular modes after parsing. The total number of intra prediction modes for a certain block is unchanged, i.e., 67, and the intra mode coding is unchanged.

To support these prediction directions, the top reference with length 2W+1, and the left reference with length 2H+1, are defined as shown in FIG. 2.

The mode number of replaced mode in wide-angular direction mode is dependent on the aspect ratio of a block. The replaced intra prediction modes are illustrated in Table 2-1.

TABLE 2-1 Intra prediction modes replaced by wide-angular modes Condition Replaced intra prediction modes W/H == 2 Modes 2, 3, 4, 5, 6, 7 W/H > 2 Modes 2, 3, 4, 5, 6, 7, 8, 9, 10, 11 W/H == 1 None H/W == 1/2 Modes 61, 62, 63, 64, 65, 66 H/W < 1/2 Mode 57, 58, 59, 60, 61, 62, 63, 64, 65, 66

As shown in FIG. 3, two vertically-adjacent predicted samples may use two non-adjacent reference samples in the case of wide-angle intra prediction. Hence, low-pass reference samples filter and side smoothing are applied to the wide-angle prediction to reduce the negative effect of the increased gap Δp_(α).

2.3 Position Dependent Intra Prediction Combination

In the VTM2, the results of intra prediction of planar mode are further modified by a position dependent intra prediction combination (PDPC) method. PDPC is an intra prediction method which invokes a combination of the un-filtered boundary reference samples and HEVC style intra prediction with filtered boundary reference samples. PDPC is applied to the following intra modes without signaling: planar, DC, horizontal, vertical, bottom-left angular mode and its eight adjacent angular modes, and top-right angular mode and its eight adjacent angular modes.

The prediction sample pred(x,y) is predicted using an intra prediction mode (DC, planar, angular) and a linear combination of reference samples according to the Equation as follows:

pred(x,y)=(wL×R _(−1,y) +wT×R _(x,−1) −wTL×R _(−1,−1)+(64−wL−wT+wTL)×pred(x,y)+32)

where R_(x,−1), R_(−1,y) represent the reference samples located at the top and left of current sample (x, y), respectively, and R_(−1,−1) represents the reference sample located at the top-left corner of the current block.

If PDPC is applied to DC, planar, horizontal, and vertical intra modes, additional boundary filters are not needed, as required in the case of HEVC DC mode boundary filter or horizontal/vertical mode edge filters.

FIG. 4 illustrates the definition of reference samples (R_(x,−1), R_(−1,y) and R_(−1,−1)) for PDPC applied over various prediction modes. The prediction sample pred (x′, y′) is located at (x′, y′) within the prediction block. The coordinate x of the reference sample R_(x,−1) is given by: x=x′+y′+1, and the coordinate y of the reference sample R_(−1,y) is similarly given by: y=x′+y′+1.

The PDPC weights are dependent on prediction modes and are shown in Table 2-2.

TABLE 2-2 Example of PDPC weights according to prediction modes Prediction modes wT wL wTL Diagonal 16 >> ((y′ << 1) >> 16 >> ((x′ << 1) >> 0 top-right shift) shift) Diagonal 16 >> ((y′ << 1) >> 16 >> ((x′ << 1) >> 0 bottom-left shift) shift) Adjacent 32 >> ((y′ << 1) >> 0 0 diagonal shift) top-right Adjacent 0 32 >> ((x′ << 1) >> 0 diagonal shift) bottom-left

3. Examples of Problems Solved By Embodiments

When performing intra prediction, usually, linear model is used. Higher-order polynomial models are not used.

4. Examples of Embodiments

The detailed techniques below should be considered as examples to explain general concepts. These techniques should not be interpreted in a narrow way. Furthermore, these techniques can be combined in any manner.

Suppose the n-order polynomial model in one variable is f(x)=Σ_(k=0) ^(n)a_(k)x^(k), and the n-order polynomial model in two variables is f(x, y)=Σ_(k=0) ^(n)a_(k)x^(k)+Σ_(k=0) ^(n)b_(k)y^(k)+Σ_(k=1) ^(n−1)c_(k)x^(k)y^(n−k). Here, a_(k), b_(k), c_(k) indicates the k-th weighting factor associated with x^(k), y^(k), x^(k)y^(n−k), respectively.

N-Order Polynomial Model In One Variable

-   1. It is proposed that n-order polynomial model in one variable may     be used for intra prediction, wherein n>=0.     -   a. In one example, x may represent the distance between the         sample to be predicted and the left boundary of the current         block along the horizontal direction;     -   b. In one example, x may represent the distance between the         sample to be predicted and the top boundary of the current block         along the vertical direction;     -   c. In one example, x may represent the distance between the         sample to be predicted and the left or top boundary of the         current block along the angular prediction direction as         illustrated in FIG. 5;     -   d. In one example, multiple sets of parameters may be derived         for the polynomial model, and each set of parameters is applied         to one set of samples.         -   i. For example, one set of samples may be defined to be             samples in the same line along a certain prediction             direction, an example is illustrated in FIG. 5.     -   e. In one example, a set of parameters may be derived for each         sample within the current block.     -   f. In one example, n is equal to 3 and f(x)=a₀+a₁x+a₂x²+a₃x³.     -   g. In one example, n is equal to 2 and f(x)=a₀+a₁x+a₂x².     -   h. In one example, some parameters (for example, a₀) may be         assumed to be zero and are not derived. -   2. It is proposed that different sets of neighboring samples may be     used when deriving different sets of parameters for the polynomial     model.     -   a. In one example, M (M>0) neighboring samples along a given         prediction direction may be used to derive one set of         parameters, an example is illustrated in FIG. 6A-D. In this         case, x may be defined as the (relative) position along the         prediction direction.     -   b. In one example, M neighboring samples within the same row         or/and neighboring samples within the same column of the current         sample may be used to derive one set of parameters, an example         is illustrated in FIG. 6E and FIG. 6F. In this case, x may be         defined as the (relative) horizontal (or vertical) position of         the sample.     -   c. In one example, for a prediction direction, if there are         available neighboring samples in both the above row and the left         column, different sets of parameters may be derived for samples         in the same prediction line. An example is illustrated in FIGS.         6G and 6H.     -   d. In one example, N+1 (i.e., M=N+1) neighboring samples may be         used for deriving parameters of N-order polynomial model.     -   e. In one example, more than N+1 (i.e., M>N+1) neighboring         samples may be used for deriving parameters of N-order         polynomial model.     -   f. In one example, M may be different for different sets of         samples.     -   g. In one example, neighboring samples used for deriving         polynomial model parameters may be selected according to the         distance between the neighboring samples and the sample to be         predicted.     -   h. It is proposed that whether and how to derive parameters from         neighbouring reconstructed samples may depend on whether         specific neighbouring reconstructed samples are available or         not.         -   i. A neighbouring reconstructed sample may be marked as             “unavailable” if it has not been decoded yet.         -   ii. A neighbouring reconstructed sample may be marked as             “unavailable” if it is not in the same slice/tile             group/tile/CTU line.         -   iii. A neighbouring reconstructed sample may be marked as             “unavailable” if it is not intra-coded.

N-Order Polynomial Model In Two Variables

-   3. It is proposed that n-order polynomial model in two variables may     be used for intra prediction, wherein n>=0.     -   a. In one example, one sets of parameters may be derived for the         polynomial model and is applied to all samples.     -   b. In one example, multiple sets of parameters may be derived         for the polynomial model, and each set of parameters is applied         to one set of samples.     -   c. In one example, a set of parameters may be derived for each         sample within the current block.     -   d. In one example, x may represent the distance between the         sample to be predicted and the left boundary of the current         block along the horizontal direction; y may represent the         distance between the sample to be predicted and the top boundary         of the current block along the vertical direction;     -   e. In one example, x may represent the distance between the         sample to be predicted and the left or top boundary of the         current block along the angular prediction direction as         illustrated in FIG. 5; y may represent the distance between the         sample to be predicted and the left or top boundary of the         current block along the direction perpendicular to the angular         prediction direction;     -   f. In one example, some parameters (for example, c_(k)) may be         assumed to be zero and are not derived. -   4. It is proposed that different sets of neighboring samples may be     used when deriving different sets of parameters for the polynomial     model.     -   g. In one example, M neighboring samples around a given         prediction direction may be used to derive one set of         parameters, an example is illustrated in FIGS. 7A-7D.     -   h. In one example, M neighboring samples around one row or/and         column may be used to derive one set of parameters for each         sample, an example is illustrated in FIGS. 7E-F.     -   i. In one example, for a prediction direction, if there are         available neighboring samples in both above row and left column,         different sets of parameters may be derived for samples in the         same prediction line. An example is illustrated in FIGS. 7G-7K.     -   j. In one example, M may be different for different sets of         samples.     -   k. In one example, only parameters a_(k) and b_(k) are derived         and parameter ck are assumed to be zero.     -   l. In one example, neighboring samples used for deriving         polynomial model parameters may be selected according to the         distance between the neighboring samples and the sample to be         predicted.     -   m. In one example, neighboring samples used for deriving         polynomial model parameters may be selected according to the         intra prediction modes.

N-Order Polynomial Model for Cross-Component Prediction

-   5. It is proposed that n-order polynomial model (e.g., in one     variable) may be used for cross-component prediction, wherein n>=0.     -   a. In one example, x may represent the sample value of one color         component (e.g., Cb) and f(x) may represent the sample value of         another color component (e.g. Y).     -   b. When deriving parameters of the polynomial model, x may         represent neighboring sample values of one color component         (e.g., Cb) and f(x) may represent the corresponding neighboring         sample values of another color component (e.g. Y).     -   c. In one example, the sample values may be processed by filters         before being used for deriving parameters of the polynomial         model.     -   d. In one example, different parameters may be derived for         different color components such as Y, Cb and Cr.

N-Order Polynomial Model for Illumination Compensation

-   6. It is proposed that n-order polynomial model (e.g., in one     variable) may be used for illumination compensation, wherein n>=0.     Suppose MV of current blocks is my.     -   a. In one example, x may represent the reference sample value         and f(x) may represent the predicted sample value.     -   b. When deriving parameters of the polynomial model, f(x) may         represent the sample value of one neighboring sample and x may         represent the sample value of its corresponding reference sample         identified by mv.         -   i. Alternatively, f(x) may represent the sample value of one             neighboring sample and x may represent the sample value of             its corresponding reference sample identified by modified             my, for example, integer part of mv.     -   c. In one example, the sample values may be processed by filters         before being used for deriving parameters of the polynomial         model.     -   d. In one example, different parameters may be derived for         different color components such as Y, Cb and Cr.

N-Order Polynomial Model for Multi-Hypothesis Inter Prediction

-   7. It is proposed that n-order polynomial model (e.g., in one     variable) may be used for multi-hypothesis inter prediction, wherein     n>=0.     -   a. In one example, x may represent the temporal distance between         a reference picture and the current picture, and f(x) may         represent the predicted sample value or/and reference sample         value of some color component.     -   b. When deriving parameters of the polynomial model, only         reference sample values are used.     -   c. In one example, the sample values may be processed by filters         before being used for deriving parameters of the polynomial         model.     -   d. In one example, different parameters may be derived for         different color components such as Y, Cb and Cr.

Other Parts

-   8. It is proposed that neighboring samples may be processed by     filters before being used for deriving parameters of the polynomial     model. -   9. It is proposed that neighboring samples in fractional positions     may be used for deriving parameters of the polynomial model, and     such neighboring samples may be interpolated by using neighboring     samples in integer positions. -   10. The parameters (e.g., a_(k), b_(k), c_(k)) of the polynomial     model may be derived from one color component, and utilized for     coding/decoding another color component.     -   a. Alternatively, furthermore, the parameters may be fixed for         all samples within one block. -   11. The neighboring samples may be firstly downsampled before being     used for deriving parameters of the polynomial model. -   12. Polynomial model-based intra prediction method may be treated as     a new intra prediction mode in addition to current existing intra     prediction mode (e.g., 67 modes in VVC).     -   b. Alternatively, Polynomial model-based intra prediction method         may be treated as a new way to derive intra prediction blocks in         addition to conventional ways. In this case, for each intra         prediction mode, or partial of allowed intra prediction modes,         it may select whether to use the polynomial model-based intra         prediction method or not. -   13. A polynomial model on/off flag may be signaled at block/CU/slice     header/tile header/VPS/PPS/SPS to indicate whether proposed method     is employed or not.     -   a. In one example, when encoding the block/CU level polynomial         model flag, context adaptive arithmetic binary coding may be         used, and one or more context may be used.         -   i. For example, one context is used.         -   ii. For example, more than one contexts may be used, and             selection of the context may depend on the polynomial model             flag of neighboring blocks.     -   b. In one example, for a decoded intra prediction mode, this         flag may be further coded/decoded to tell whether the         conventional intra prediction method or polynomial model-based         intra prediction method is utilized for decoding the current         block.     -   c. In one example, such a flag may be firstly decoded before         decoding the intra prediction mode. If this flag indicates that         polynomial model-based intra prediction method is utilized for         decoding the current block, there is no need to further decode         the intra prediction mode. In this case, polynomial model-based         intra prediction method is treated as a new intra prediction         mode. -   14. Some parameters of the polynomial model may be assumed to be     default values (e.g., zero) and are not derived. -   15. The above methods may be applied under certain conditions and     may be implicitly disabled in other cases.     -   d. For example, it may be applied for certain color components,         e.g., only luma color component.     -   e. For example, it may be applied for certain block size/block         shape etc. al     -   f. For example, it may be applied for certain intra prediction         modes and disallowed for other remaining intra prediction modes.     -   g. When it is disallowed under other conditions, the indication         of above methods are not signaled. -   16. The results of n-order polynomial model may be further clipped     before being used as the prediction values.     -   c. In one example, f(x)=Clip3((Σ_(k=0) ^(n)a_(k)x^(k)+off)>>S),         f(x, y)=Clip3((Σ_(k=0) ^(n)a_(k)x^(k)+Σ_(k=0)         ^(n)b_(k)y^(k)+Σ_(k=1) ^(n−1)c_(k)x^(k)y^(n−k)+off)>>S), where         off may be 0 or (1<<S)>>1. Clip3 is a clipping operation to clip         the prediction value valid. For example, Clip3(x)=max(0,         min(MaxValue, x)).     -   d. In one example, MaxValue may be defined as (1<<Bitdepth)−1.     -   e. In one example, MaxValue may be changed from slice to         slice/tile to tile/picture to picture, e.g., it may represent         the maximally allowed value for a given color component/a given         block/a given CTU/a given CTU row.

FIG. 8 is a block diagram of a video processing apparatus 800. The apparatus 800 may be used to implement one or more of the methods described herein. The apparatus 800 may be embodied in a smartphone, tablet, computer, Internet of Things (IoT) receiver, and so on. The apparatus 800 may include one or more processors 802, one or more memories 804 and video processing hardware 806. The processor(s) 802 may be configured to implement one or more methods described in the present document. The memory (or memories) 804 may be used for storing data and code used for implementing the methods and techniques described herein. The video processing hardware 806 may be used to implement, in hardware circuitry, some techniques described in the present document.

FIG. 10 is a flowchart for a method 1000 of video processing. The method 1000 includes performing (1005) a conversion between a current video block and a bitstream representation of the current video block using an intra-prediction coding scheme based on an n-order polynomial model using at least one variable associated with the current video block, where n is an integer greater than or equal to zero, wherein the conversion includes generating the current video block from the bitstream representation or generating the bitstream representation from the current video block.

FIG. 11 is a flowchart for a method 1100 of video processing. The method 1100 includes performing (1105) a conversion between a current video block and a bitstream representation of the current video block using an intra-prediction coding scheme based on an n-order polynomial model using a first variable associated with the current video block, where n is an integer greater than or equal to zero, wherein the conversion includes generating the current video block from the bitstream representation or generating the bitstream representation from the current video block, wherein cross-component prediction is applied by using the n-order polynomial model.

With reference to methods 1000 and 1100, some examples of intra prediction using a polynomial model and their use are described in Section 4 of the present document. For example, as described in Section 4, an n-order polynomial model with one or two variables can be used.

With reference to methods 1000 and 1100, the video block may be encoded in the video bitstream in which bit efficiency may be achieved by using a bitstream generation rule related to intra prediction.

FIG. 12 is a flowchart for a method 1200 of video processing. The method 1200 includes performing (1205) a conversion between a current video block and a bitstream representation of the current video block using an inter-prediction coding scheme based on an n-order polynomial model using a first variable associated with the current video block, where n is an integer greater than or equal to zero, wherein the conversion includes generating the current video block from the bitstream representation or generating the bitstream representation from the current video block; and performing (1207) illumination compensation for the current video block using the n-order polynomial model during the conversion.

FIG. 13 is a flowchart for a method 1300 of video processing. The method 1300 includes performing (1305) a conversion between a current video block and a bitstream representation of the current video block using an inter-prediction coding scheme based on an n-order polynomial model using a first variable associated with the current video block, where n is an integer greater than or equal to zero, wherein the conversion includes generating the current video block from the bitstream representation or generating the bitstream representation from the current video block; and performing (1307) multi-hypothesis inter prediction using the n-order polynomial model during the conversion.

Various embodiments and techniques described throughout the present document may be described using the following clause based format.

1.1. A method for processing video, comprising: performing a conversion between a current video block and a bitstream representation of the current video block using an intra-prediction coding scheme based on an n-order polynomial model using at least one variable associated with the current video block, where n is an integer greater than or equal to zero, wherein the conversion includes generating the current video block from the bitstream representation or generating the bitstream representation from the current video block.

1.2. The method of example 1.1, wherein the n-order polynomial model uses one variable.

1.3. The method of example 1.2, wherein the one variable represents one of a distance between a sample to be predicted and a left boundary of the current video block along a horizontal direction, a distance between a sample to be predicted and a top boundary of the current video block along a vertical direction, a distance between a sample to be predicted and a left or a top boundary of the current video block along an angular prediction direction.

1.4. The method of example 1.1, wherein the n-order polynomial model uses two variables.

1.5. The method of example 1.4, wherein one variable of the two variables represents a distance between a sample to be predicted and a left boundary of the current video block along a horizontal direction, and another variable of the two variables represents a distance between the sample and a top boundary of the current video block along a vertical direction.

1.6. The method of example 1.4, wherein one variable of the two variables represents a distance between a sample to be predicted and a left or a top boundary of the current video block along an angular prediction direction, and another variable of the two variables represents a distance between the sample and the left or the top boundary of the current video block along a direction perpendicular to the angular prediction direction.

1.7. The method of any of examples 1.1-1.6, wherein multiple sets of parameters are derived for the n-order polynomial model, each of the multiple sets of parameters to be applied to one set of samples of the current video block.

1.8. The method of example 1.7, wherein the one set of samples of the current video block includes samples in a same line along a certain prediction direction.

1.9. The method of any of examples 1.1-1.6, wherein a set of parameters is derived for the n-order polynomial model, wherein the set of parameters are applied to each sample of the current video block.

1.10. The method of any one of examples 1.7-1.9, wherein some parameters of the multiple sets of parameters for the n-order polynomial model are forced to be zeros.

1.11. The method of example 1.2 or 1.3, wherein n is 3, and the n-order polynomial model is f(x)=a₀+a₁x+a₂x²+a₃x³, wherein x is the one variable.

1.12. The method of example 1.2, wherein n is 2, and the n-order polynomial model is f(x)=a₀+a₁x+a₂x², wherein x is the one variable.

1.13. The method of any of claims 1.4-1.6, wherein the n-order polynomial model is f(x, y)=Σ_(k=0) ^(n)a_(k)x^(k)+Σk=0 ^(n)b_(k)y^(k)+Σ_(k=1) ^(n−1)c_(k)x^(k)y^(n−k), wherein x is one variable of the two variables and y is another variable of the two variables.

1.14. The method of example 1.13, wherein a_(k) and b_(k) are derived, and wherein c_(k) is zero.

1.15. The method of any one of claims 1.11-1.14, wherein f(x) represents predicted sample values of samples of the current video block.

1.16. The method of any of claims 1.7-1.8, wherein a first set of neighboring samples is used to derive a first set of parameters, and a second set of neighboring samples which is different from the first set of neighboring samples is used to derive a second set of parameters which is different from the first set of parameters.

1.17. The method of example 1.16, wherein the n-order polynomial model uses one variable, wherein the first set of neighboring samples are in a first line along a prediction direction and the second set of neighboring samples are in a second line along the prediction direction, wherein the first line is different from the second line.

1.18. The method of example 1.16, wherein the n-order polynomial model uses two variables, wherein the first set of neighboring samples are in a first line along a prediction direction or in lines adjacent to the first line along the prediction direction, and the second set of neighboring samples are in a second line along the prediction direction or in lines adjacent to the second line along the prediction direction.

1.19. The method of any of examples 1.17-1.18, wherein the prediction direction is one of an angular direction, a horizontal direction and a vertical direction.

1.20. The method of any one of examples 1.16-1.19, wherein the samples of the current video block in the first line along a prediction direction is predicted using the first set of parameters and the samples of the current video block in the second line along the prediction direction is predicted using the second set of parameters.

1.21. The method of example 1.16, wherein for a prediction direction, if there are available neighboring samples in both above row and left column in relation to a current sample, different sets of parameters are derived for samples in a prediction line in the prediction direction.

1.22. The method of any of examples 1.16-1.21, wherein, for the n-order polynomial model, n+1 neighboring samples are used to derive parameters of the n-order polynomial model, where n is an integer greater than or equal to zero.

1.23. The method of any of examples 1.16-1.22, wherein for the n-order polynomial model, more than n+1 neighboring samples are used to derive parameters of the n-order polynomial model, where n is an integer greater than or equal to zero.

1.24. The method of any one of examples 1.16-1.23, wherein the first set of neighboring samples includes a first number of samples, and the second set of neighboring samples includes a second number of samples, wherein the first number and the second number are different.

1.25. The method of any of examples 1.16-1.24, wherein one or both of the first set of neighboring samples and the second set of neighboring samples are selected based on at least one of a distance between the neighboring samples and a current sample to be predicted, and the intra-prediction coding scheme that is applied.

1.26. The method of example 1.16, wherein the deriving the first set of parameters and the second set of parameters is based on a determination regarding availability of neighboring reconstructed samples.

1.27. The method of example 1.25, wherein a neighboring sample is determined to be unavailable if it has not been decoded.

1.28. The method of example 1.25, wherein a neighboring sample is determined to be unavailable if it is not in a same slice, a same tile group, a same tile, or a same coding tree unit (CTU) line with the current sample.

1.29. The method of example 1.25, wherein a neighboring sample is determined to be unavailable if it is not intra-coded.

1.30. A method for processing video, comprising: performing a conversion between a current video block and a bitstream representation of the current video block using an intra-prediction coding scheme based on an n-order polynomial model using a first variable associated with the current video block, where n is an integer greater than or equal to zero, wherein the conversion includes generating the current video block from the bitstream representation or generating the bitstream representation from the current video block, wherein cross-component prediction is applied by using the n-order polynomial model.

1.31. The method of example 1.30, wherein the n-order polynomial model is f(x)=a₀+a₁x+a₂x²+a₃x³ or f(x)=a₀+a₁x+a₂x², wherein x is the first variable, x represents a sample value of a first color component, and f(x) represents a predicted sample value of a second color component, the first color component and the second color component being different.

1.32. The method of example 1.30, wherein the n-order polynomial model is f(x)=a₀+a₁x+a₂x²+a₃x³ or f(x)=a₀+a₁x+a₂x², wherein x is the first variable, and when deriving the parameters of the n-order polynomial model, x represents a neighboring sample values of a first color component of the current video block, and f(x) represents the corresponding neighboring sample values of a second color component of the current video block, the first color component and the second color component being different.

1.33. The method of any of examples 1.30-1.32, wherein neighboring sample values of the first color component and the second color component are processed by filters to generate filtered sample values, and the filtered sample values are used to derive parameters of the n-order polynomial model.

1.34. The method of example 1.30, wherein different parameters are derived for different color components.

1.35. The method of any of examples 1.1-1.34, wherein neighboring samples are processed by filters to generate filtered neighboring samples, and the filtered neighboring samples are used to derive the parameters of the n-order polynomial model.

1.36. The method of any of examples 1.1-1.34, wherein neighboring samples in fractional positions are used for deriving the parameters, and the fractional neighboring samples are interpolated using neighboring samples in integer positions.

1.37. The method of any of examples 1.1-1.34, wherein the parameters of the n-order polynomial model are derived from a color component and used for other color components.

1.38. The method of any of examples 1.1-1.34, wherein the parameters of the n-order polynomial model are fixed for all samples in one block.

1.39. The method of any of examples 1.1-1.34, wherein neighboring samples are downsampled before being used to derive the parameters of the n-order polynomial model.

1.40. The method of any of examples 1.1-1.34, wherein the method is used as a new intra-prediction mode in addition to a current existing intra-prediction mode.

1.41. The method of any of examples 1.1-1.34, wherein the method is used as a new way to derive intra prediction blocks in addition to current existing ways, and wherein for each intra prediction mode, or partial of allowed intra prediction modes, a syntax indicating whether to use the polynomial model-based intra prediction method or not is signaled.

1.42. The method of any of examples 1.1-1.35, wherein a flag that indicates usage of the n-order polynomial model is signaled with a block, a coding unit (CU), a slice header, a tile header, a video parameter set (VPS), a sequence parameter set (SPS), or a picture parameter set (PPS).

1.43. The method of example 1.42, wherein context adaptive arithmetic binary coding is used to encode the flag.

1.44. The method of example 1.43, wherein one or more contexts are used to encode the flag, and when more than one contexts are used, the selection of the contexts are based on the polynomial model flag of neighboring video blocks.

1.45. The method of any of examples 1.42-1.44, wherein the flag further indicates usage of a conventional intra-prediction method or a polynomial model-based intra-prediction method for the current video block.

1.46. The method of any of examples 1.42-1.44, wherein the flag is decoded before decoding an intra-prediction mode, and wherein if the flag indicates that polynomial model-based intra prediction method is used for decoding the current video block, refraining from decoding the intra prediction mode.

1.47. The method of any of examples 1.1-1.34, wherein some parameters of the n-order polynomial model are default values and are not derived.

1.48. The method of any of examples 1.1-1.34, wherein the n-order polynomial model is applied on only luma color components.

1.49. The method of any of examples 1.1-1.34, wherein the n-order polynomial model is used based on a block size or a block shape of the current video block.

1.50. The method of any of examples 1.1-1.34, wherein the method is used for certain intra-prediction modes and disabled for other remaining intra-prediction modes, and when the method is disable, refraining from signaling any indication of the method.

1.51. The method of any of examples 1.1-1.34, wherein the generated value by applying the n-order polynomial model is clipped before being used as prediction value.

1.52. The method of example 1.51, wherein f(x)=Clip3((Σ_(k=0) ^(n)a_(k)x^(k)+off)>>S), and f(x,y)=Clip3((Σ_(k=0) ^(n)a_(k)x^(k)+Σ_(k=0) ^(n)b_(k)y^(k)+Σ_(k=1) ^(n−1)c_(k)x^(k)y^(n−k)+off)>>S), where off is 0, or off=2(S−1), and Clip3 is a function to clip a prediction value.

1.53. The method of example 1.52, wherein Clip3(x)=max(0, min(MaxValue, x)), and wherein MaxValue is 2Bitdepth−1 and represents maximally allowed value for a given color component/a given block/a given CTU/a given CTU row.

1.54. The method of example 1.52, wherein Clip3(x)=max(0, min(MaxValue, x)), and wherein MaxValue is changed from slice to slice, or from tile to tile, or from picture to picture, wherein MaxValue represents maximally allowed value for a given color component/a given block/a given CTU/a given CTU row.

1.55. A video decoding apparatus comprising a processor configured to implement a method recited in one or more of examples 1.1 to 1.54.

1.56. A video encoding apparatus comprising a processor configured to implement a method recited in one or more of examples 1.1 to 1.54.

1.57. A computer program product having computer code stored thereon, the code, when executed by a processor, causes the processor to implement a method recited in any of examples 1.1 to 1.54.

2.1. A method for processing video, comprising: performing a conversion between a current video block and a bitstream representation of the current video block using an inter-prediction coding scheme based on an n-order polynomial model using a first variable associated with the current video block, where n is an integer greater than or equal to zero, wherein the conversion includes generating the current video block from the bitstream representation or generating the bitstream representation from the current video block; and performing illumination compensation for the current video block using the n-order polynomial model during the conversion.

2.2. The method of example 2.1, wherein n is 3, and the n-order polynomial model is f(x)=a₀+a₁x+a₂x²+a₃x³, wherein a_(i), where i=0, 1, 2, 3, is a parameter of the n-order polynomial model, and x is the first variable.

2.3. The method of example 2.1, wherein n is 2, and the n-order polynomial model is f(x)=a₀+a₁x+a₂x², wherein a_(i), where i=0, 1, 2, is a parameter of the n-order polynomial model, and x is the first variable.

2.4. The method of example 2.2 or example 2.3, wherein x represents a reference sample value of a first sample of the current video block, and f(x) represents a predicted sample value of the first sample.

2.5. The method of example 2.2 or example 2.3, wherein the parameters are derived using at least one reconstructed value of at least one second sample and at least one reference sample of the at least one second sample based on the n-order polynomial model, and wherein the second sample is a neighboring sample of the current video block.

2.6. The method of example 2.5, wherein when deriving the parameters, f(x) represents the reconstructed value of the second sample, and x represents a reference sample value of the second sample, and wherein the reference sample is identified by a motion vector (MV) of the current video block.

2.7. The method of example 2.5, wherein when deriving the parameters, f(x) represents the reconstructed value of the second sample, and x represents a reference sample value of the second sample, wherein the reference sample of the second sample is identified by a modified value of a MV of the current video block.

2.8. The method of example 2.7, wherein the modified value is the integer part of the MV.

2.9. The method of any of examples 2.5-2.8, wherein the reconstructed value and the reference sample value of the second samples are processed by filters to generate filtered sample values, and the filtered sample values are used to derive the parameters of the n-order polynomial model.

2.10. The method of any of examples 2.1-2.9, wherein different parameters are derived for different color components.

2.11. A method for processing video, comprising: performing a conversion between a current video block and a bitstream representation of the current video block using an inter-prediction coding scheme based on an n-order polynomial model using a first variable associated with the current video block, where n is an integer greater than or equal to zero, wherein the conversion includes generating the current video block from the bitstream representation or generating the bitstream representation from the current video block; and performing multi-hypothesis inter prediction using the n-order polynomial model during the conversion.

2.12. The method of example 2.11, wherein n is 3, and the n-order polynomial model is f(x)=a₀+a₁x+a₂x²+a₃x³, wherein a_(i), where i=0, 1, 2,3, is a parameter of the n-order polynomial model, and x is the first variable.

2.13. The method of example 2.11, wherein n is 2, and the n-order polynomial model is f(x)=a₀+a₁x+a₂x², wherein a_(i), where i=0, 1, 2, is a parameter of the n-order polynomial model, and x is the first variable.

2.14. The method of example 2.12 or example 2.13, wherein x represents a temporal distance between a reference picture and a current picture related to the current video block, and f(x) represents a predicted sample value of a color component.

2.15. The method of example 2.12 or 2.13, wherein the parameters of the n-order polynomial model are derived using reference sample values of multiple reference blocks of the current video block and multiple temporal distances each of which is a temporal distance between one reference picture related to one of the multiple reference blocks and a current picture related to the current video block.

2.16. The method of example 2.12 or example 2.13, wherein the parameters of the n-order polynomial model are derived using reference sample values of multiple reference blocks of the current video block and the temporal distance between different reference pictures related to the multiple reference blocks.

2.17. The method of example 2.15 or example 2.16, wherein the reference sample values are processed by filters to generate filtered sample values, and the filtered sample values are used to derive the parameters of the n-order polynomial model.

2.18. The method of any one of examples 2.12-2.17, wherein different parameters of the n-order polynomial model are derived for different color components.

2.19. A video decoding apparatus comprising a processor configured to implement a method recited in one or more of examples 2.1 to 2.18.

2.20. A video encoding apparatus comprising a processor configured to implement a method recited in one or more of examples 2.1 to 2.18.

2.21. A computer program product having computer code stored thereon, the code, when executed by a processor, causes the processor to implement a method recited in any of examples 2.1 to 2.18.

It will be appreciated that the disclosed techniques may be embodied in video encoders or decoders to improve compression efficiency.

The disclosed and other solutions, examples, embodiments, modules and the functional operations described in this document can be implemented in digital electronic circuitry, or in computer software, firmware, or hardware, including the structures disclosed in this document and their structural equivalents, or in combinations of one or more of them. The disclosed and other embodiments can be implemented as one or more computer program products, i.e., one or more modules of computer program instructions encoded on a computer readable medium for execution by, or to control the operation of, data processing apparatus. The computer readable medium can be a machine-readable storage device, a machine-readable storage substrate, a memory device, a composition of matter effecting a machine-readable propagated signal, or a combination of one or more them. The term “data processing apparatus” encompasses all apparatus, devices, and machines for processing data, including by way of example a programmable processor, a computer, or multiple processors or computers. The apparatus can include, in addition to hardware, code that creates an execution environment for the computer program in question, e.g., code that constitutes processor firmware, a protocol stack, a database management system, an operating system, or a combination of one or more of them. A propagated signal is an artificially generated signal, e.g., a machine-generated electrical, optical, or electromagnetic signal, which is generated to encode information for transmission to suitable receiver apparatus.

A computer program (also known as a program, software, software application, script, or code) can be written in any form of programming language, including compiled or interpreted languages, and it can be deployed in any form, including as a stand-alone program or as a module, component, subroutine, or other unit suitable for use in a computing environment. A computer program does not necessarily correspond to a file in a file system. A program can be stored in a portion of a file that holds other programs or data (e.g., one or more scripts stored in a markup language document), in a single file dedicated to the program in question, or in multiple coordinated files (e.g., files that store one or more modules, sub programs, or portions of code). A computer program can be deployed to be executed on one computer or on multiple computers that are located at one site or distributed across multiple sites and interconnected by a communication network.

The processes and logic flows described in this document can be performed by one or more programmable processors executing one or more computer programs to perform functions by operating on input data and generating output. The processes and logic flows can also be performed by, and apparatus can also be implemented as, special purpose logic circuitry, e.g., an FPGA (field programmable gate array) or an ASIC (application specific integrated circuit).

Processors suitable for the execution of a computer program include, by way of example, both general and special purpose microprocessors, and any one or more processors of any kind of digital computer. Generally, a processor will receive instructions and data from a read only memory or a random-access memory or both. The essential elements of a computer are a processor for performing instructions and one or more memory devices for storing instructions and data. Generally, a computer will also include, or be operatively coupled to receive data from or transfer data to, or both, one or more mass storage devices for storing data, e.g., magnetic, magneto optical disks, or optical disks. However, a computer need not have such devices. Computer readable media suitable for storing computer program instructions and data include all forms of non-volatile memory, media and memory devices, including by way of example semiconductor memory devices, e.g., EPROM, EEPROM, and flash memory devices; magnetic disks, e.g., internal hard disks or removable disks; magneto optical disks; and CD ROM and DVD-ROM disks. The processor and the memory can be supplemented by, or incorporated in, special purpose logic circuitry.

While this patent document contains many specifics, these should not be construed as limitations on the scope of any invention or of what may be claimed, but rather as descriptions of features that may be specific to particular embodiments of particular inventions. Certain features that are described in this patent document in the context of separate embodiments can also be implemented in combination in a single embodiment. Conversely, various features that are described in the context of a single embodiment can also be implemented in multiple embodiments separately or in any suitable subcombination. Moreover, although features may be described above as acting in certain combinations and even initially claimed as such, one or more features from a claimed combination can in some cases be excised from the combination, and the claimed combination may be directed to a subcombination or variation of a subcombination.

Similarly, while operations are depicted in the drawings in a particular order, this should not be understood as requiring that such operations be performed in the particular order shown or in sequential order, or that all illustrated operations be performed, to achieve desirable results. Moreover, the separation of various system components in the embodiments described in this patent document should not be understood as requiring such separation in all embodiments.

Only a few implementations and examples are described and other implementations, enhancements and variations can be made based on what is described and illustrated in this patent document. 

1. A method for processing video, comprising: performing a conversion between a current video block and a bitstream of the current video block using an inter-prediction coding scheme based on an n-order polynomial model using a first variable associated with the current video block, where n is an integer greater than or equal to zero, wherein the conversion includes generating the current video block from the bitstream or generating the bitstream from the current video block; and performing illumination compensation for the current video block using the n-order polynomial model during the conversion.
 2. The method of claim 1, wherein n is 3, and the n-order polynomial model is f(x)=a₀+a₁x+a₂x²+a₃x³, wherein a_(i), where i=0, 1, 2, 3, is a parameter of the n-order polynomial model, and x is the first variable.
 3. The method of claim 1, wherein n is 2, and the n-order polynomial model is f(x)=a₀+a₁x+a₂x², wherein a_(i), where i=0, 1, 2, is a parameter of the n-order polynomial model, and x is the first variable.
 4. The method of claim 2, wherein x represents a reference sample value of a first sample of the current video block, and f(x) represents a predicted sample value of the first sample.
 5. The method of claim 3, wherein x represents a reference sample value of a first sample of the current video block, and f(x) represents a predicted sample value of the first sample.
 6. The method of claim 2, wherein the parameters are derived using at least one reconstructed value of at least one second sample and at least one reference sample of the at least one second sample based on the n-order polynomial model, and wherein the second sample is a neighboring sample of the current video block.
 7. The method of claim 3, wherein the parameters are derived using at least one reconstructed value of at least one second sample and at least one reference sample of the at least one second sample based on the n-order polynomial model, and wherein the second sample is a neighboring sample of the current video block.
 8. The method of claim 6, wherein when deriving the parameters, f(x) represents the reconstructed value of the second sample, and x represents a reference sample value of the second sample, and wherein the reference sample is identified by a motion vector (MV) of the current video block.
 9. The method of claim 6, wherein when deriving the parameters, f(x) represents the reconstructed value of the second sample, and x represents a reference sample value of the second sample, wherein the reference sample of the second sample is identified by a modified value of a MV of the current video block.
 10. The method of claim 9, wherein the modified value is the integer part of the MV.
 11. The method of claim 6, wherein the reconstructed value and the reference sample value of the second samples are processed by filters to generate filtered sample values, and the filtered sample values are used to derive the parameters of the n-order polynomial model.
 12. The method of claim 1, further comprising: performing multi-hypothesis inter prediction using the n-order polynomial model during the conversion.
 13. The method of claim 12, wherein x represents a temporal distance between a reference picture and a current picture related to the current video block, and f(x) represents a predicted sample value of a color component.
 14. The method of claim 12, wherein the parameters of the n-order polynomial model are derived using reference sample values of multiple reference blocks of the current video block and multiple temporal distances each of which is a temporal distance between one reference picture related to one of the multiple reference blocks and a current picture related to the current video block.
 15. The method of claim 12, wherein the parameters of the n-order polynomial model are derived using reference sample values of multiple reference blocks of the current video block and the temporal distance between different reference pictures related to the multiple reference blocks.
 16. The method of claim 14, wherein the reference sample values are processed by filters to generate filtered sample values, and the filtered sample values are used to derive the parameters of the n-order polynomial model.
 17. The method of claim 15, wherein the reference sample values are processed by filters to generate filtered sample values, and the filtered sample values are used to derive the parameters of the n-order polynomial model.
 18. The method of claim 1, wherein different parameters of the n-order polynomial model are derived for different color components.
 19. A video processing apparatus comprising a processor and a non-transitory memory with instructions thereon, wherein the instructions upon execution by the processor, cause the processor to: perform a conversion between a current video block and a bitstream of the current video block using an inter-prediction coding scheme based on an n-order polynomial model using a first variable associated with the current video block, where n is an integer greater than or equal to zero, wherein the conversion includes generating the current video block from the bitstream or generating the bitstream from the current video block; and perform illumination compensation for the current video block using the n-order polynomial model during the conversion.
 20. A non-transitory computer-readable recording medium storing a bitstream of a video which is generated by a method performed by a video processing apparatus, wherein the method comprises: generating the bitstream using an inter-prediction coding scheme based on an n-order polynomial model using a first variable associated with the current video block, where n is an integer greater than or equal to zero; and performing illumination compensation for the current video block using the n-order polynomial model during generating the bitstream. 